Trimerization

ABSTRACT

A new P—N—P ligand is useful in ethylene oligomerizations. In combination with i) a source of chromium and ii) an activator such as methylalumoxane; the ligand of this invention may be used to prepare an oligomer product that contains a mixture of hexenes and octenes. The hexenes and octenes produced with this ligand contain very low levels of internal olefins when produced under preferred reaction conditions.

FIELD OF THE INVENTION

This invention provides a new family of P—N—P ligands. The ligands areuseful in ethylene oligomerization reactions.

BACKGROUND OF THE INVENTION

Alpha olefins are commercially produced by the oligomerization ofethylene in the presence of a simple alkyl aluminum catalyst (in the socalled “chain growth” process) or alternatively, in the presence of anorganometallic nickel catalyst (in the so called Shell Higher Olefins,or “SHOP” process). Both of these processes typically produce a crudeoligomer product having a broad distribution of alpha olefins with aneven number of carbon atoms (i.e. butene-1, hexene-1, octene-1 etc.).The various alpha olefins in the crude oligomer product are thentypically separated in a series of distillation columns. Butene-1 isgenerally the least valuable of these olefins as it is also produced inlarge quantities as a by-product in various cracking and refiningprocesses. Hexene-1 and octene-1 often command comparatively high pricesbecause these olefins are in high demand as comonomers for linear lowdensity polyethylene (LLDPE).

Technology for the selective trimerization of ethylene to hexene-1 hasbeen recently put into commercial use in response to the demand forhexene-1. The patent literature discloses catalysts which comprise achromium source and a pyrrolide ligand as being useful for thisprocess—see, for example, U.S. Pat. No. 5,198,563 (Reagen et al.,assigned to Phillips Petroleum).

Another family of highly active trimerization catalysts is disclosed byWass et al. in WO 02/04119 (now U.S. Pat. Nos. 7,143,633 and 6,800,702.The catalysts disclosed by Wass et al. are formed from a chromium sourceand a chelating diphosphine ligand and are described in further detailby Carter et al. (Chem. Comm. 2002, p 858-9). As described in the Chem.Comm. paper, these catalysts preferably comprise a diphosphine ligand inwhich both phosphine atoms are bonded to two phenyl groups that are eachsubstituted with an ortho-methoxy group. Hexene-1 is produced with highactivity and high selectivity by these catalysts.

Similar diphosphine/tetraphenyl ligands are disclosed by Blann et al. inWO04/056478 and WO 04/056479 (now US 2006/0229480 and US 2006/0173226).However, in comparison to the ligands of Wass et al., thedisphosphine/tetraphenyl ligands disclosed by Blann et al. generally donot contain polar substituents in ortho positions. The “tetraphenyl”diphosphine ligands claimed in the '480 application must not have orthosubstituents (of any kind) on all four of the phenyl groups and the“tetraphenyl” diphosphine ligands claimed in '226 are characterized byhaving a polar substituent in a meta or para position. Both of theseapproaches are shown to reduce the amount of hexenes produced andincrease the amount of octene (in comparison to the ligands of Wass etal.). However, the hexene fraction generally contains a large portion ofinternal hexenes, which is undesirable. Thus, chromium based catalystswhich contain the ligands of Blann et al. typically produce more octene(which may be advantageous if demand for octene is high) but theseligands have the disadvantage of producing a hexene stream which iscontaminated with a comparatively large amount of internal olefins.

Internal olefins are undesirable contaminants in linear low densitypolyethylene (LLDPE) production facilities because the internal olefinsare not readily incorporated into LLDPE with most transition metalcatalysts. Thus, it is preferable to remove/separate internal olefinsfrom alpha olefins if the alpha olefin is to be used in an LLDPEprocess. As will be appreciated by those skilled in the art, it iscomparatively difficult to separate hexene-1 from internal hexenes bydistillation due to the close boiling points of these hexene isomers.

Accordingly, a process which selectively produces a mixture of hexene-1and octene-1 with very low levels of internal olefins represents adesirable addition to the art.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a new family of P—N—Pligands defined by the formula:

wherein each of Ph₁, Ph₂, Ph₃ and Ph₄ is a phenyl group bonded to aphosphorus atom, with the provisos that

-   -   i) at least one of Ph₁, Ph₂, Ph₃ and Ph₄ is ortho substituted        with a halogen selected from the group consisting of fluorine,        bromine and chlorine;    -   ii) at least one of Ph₁, Ph₂, Ph₃ and Ph₄ is ortho substituted        with a polar substituent; and    -   iii) R₂ is selected from the group consisting of hydrogen, C₁₋₂₀        hydrocarbyl and silyl.

These molecules are particularly suitable for use as a ligand in aprocess to oligomerize ethylene. Potential alternative uses includeligands for hydrogenation and/or hydroformylation reactions.

Attempts to produce the new ligands by conventional condensationreactions (i.e., using a precursor amine and a precursor diphosphinechloride) were unsuccessful. Accordingly, another embodiment of thisinvention provides a new synthetic route to this family of molecules. Apreferred synthesis is described in more detail in the Examples.

Another embodiment of this invention provides a catalyst systemcomprising:

-   -   a) a transition metal selected from the group consisting of Cr,        V, Ti, Ni, and W;    -   b) A ligand defined by the formula:

-   -   wherein each of Ph₁, Ph₂, Ph₃ and Ph₄ is a phenyl group bonded        to a phosphorus atom, with the provisos that        -   i) at least one of Ph₁, Ph₂, Ph₃ and Ph₄ is ortho            substituted with a halogen selected from the group            consisting of fluorine, bromine and chlorine;        -   ii) at least one of Ph₁, Ph₂, Ph₃ and Ph₄ is ortho            substituted with a polar substituent; and        -   iii) R₂ is selected from the group consisting of hydrogen,            C₁₋₂₀ hydrocarbyl and silyl; and    -   c) an activator.

The oligomerization process of this invention may be conducted underconventional oligomerization conditions. One important advantage of thepresent invention is that the product olefins can comprise a desirablemixture of hexene and octene (in particular, greater than 80 weight % ofthe ethylene that is converted to a liquid product during the processcan be hexenes and octenes) with very low levels of internal olefins(preferably less than 15 weight % of the mixed hexene and octene streamis internal olefins) when the process is conducted under preferredtemperature and pressure conditions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Part A: Catalyst System

The catalyst system used in the process of the present invention mustcontain three essential components, namely:

(i) a source of chromium:

(ii) a defined P—N—P ligand; and

(iii) an activator.

Preferred forms of each of these components are discussed below.

Chromium Source (“Component (i)”)

Any source of chromium which allows the oligomerization process of thepresent invention to proceed may be used. Preferred chromium sourcesinclude chromium trichloride; chromium (III) 2-ethylhexanoate; chromium(III) acetylacetonate and chromium carboxyl complexes such as chromiumhexacarboxyl.

Ligand Used in the Oligomerization Process (“Component (ii)”)

In general, the ligand used in the oligomerization process of thisinvention is defined by the formula:

wherein each of Ph₁, Ph₂, Ph₃ and Ph₄ is a phenyl group bonded to aphosphorus atom, with the provisos that

-   -   i) at least one of Ph₁, Ph₂, Ph₃ and Ph₄ is ortho substituted        with a halogen selected from the group consisting of fluorine,        bromine and chlorine;    -   ii) at least one of Ph₁, Ph₂, Ph₃ and Ph₄ is ortho substituted        with a polar substituent; and    -   iii) R₂ is selected from the group consisting of hydrogen, C₁₋₂₀        hydrocarbyl and silyl.

Each halogen is preferably fluorine.

R₂ is preferably a hydrocarbyl group having from 1 to 20 carbon atoms.The analogous silyl groups may also be employed. The hydrocarbyl groupsof R₂ may contain heteroatom substituents (having a heteroatom selectedfrom O, N, P and S). Simple alkyl groups having from 1 to 12 carbonatoms are preferred. Isopropyl is particularly preferred.

As used herein, the term “polar” refers to a substituent with a dipolemoment. Examples include C₁₋₂₀ alkoxy (with methoxy, ethoxy andisopropoxy being preferred—especially methoxy); phenoxy, hydroxyl,amino, sulfate and the like. Alkoxy substituents are most preferred,especially methoxy.

In a preferred embodiment, the substituents on the four phenyl groupssatisfy another condition, namely that all of Ph₁, Ph₂, Ph₃ and Ph₄ areeither ortho substituted with a halogen (preferably fluorine) or orthosubstituted with a polar substituent (especially an alkoxy substituent).

The ortho substituents on the phenyl groups of the present ligands arecritical to the present invention. Substituents at meta or parapositions are generally less important but are contemplated within thescope of the present invention.

Activator (“Component (iii)”)

The activator (component (iii)) may be any compound that generates anactive catalyst for ethylene oligomerization with components (i) and(ii). Mixtures of activators may also be used. Suitable compoundsinclude organoaluminum compounds, organoboron compounds and inorganicacids and salts, such as tetrafluoroboric acid etherate, silvertetrafluoroborate, sodium hexafluoroantimonate and the like. Suitableorganoaluminum compounds include compounds of the formula AlR₃, whereeach R is independently C₁-C₁₂ alkyl, oxygen or halide, and compoundssuch as LiAlH₄ and the like. Examples include trimethylaluminum (TMA),triethylaluminum (TEA), tri-isobutylaluminium (TIBA),tri-n-octylaluminium, methylaluminium dichloride, ethylaluminiumdichloride, dimethylaluminium chloride, diethylaluminium chloride,ethylaluminiumsesquichloride, methylaluminiumsesquichloride, andalumoxanes. Alumoxanes are well known in the art as typically oligomericcompounds which can be prepared by the controlled addition of water toan alkylaluminium compound, for example trimethylaluminium. Suchcompounds can be linear, cyclic, cages or mixtures thereof. Commerciallyavailable alumoxanes are generally believed to be mixtures of linear andcyclic compounds. The cyclic alumoxanes can be represented by theformula [R⁶AlO]_(s) and the linear alumoxanes by the formulaR⁷(R⁸AlO)_(s) wherein s is a number from about 2 to 50, and wherein R⁶,R⁷, and R⁸ represent hydrocarbyl groups, preferably C₁ to C₆ alkylgroups, for example methyl, ethyl or butyl groups. Alkylalumoxanesespecially methylalumoxane (MAO) are preferred. (MAO is also referred toas methalumoxane and methylaluminoxane in the literature).

It will be recognized by those skilled in the art that commerciallyavailable alkylalumoxanes may contain a proportion of trialkylaluminium.For instance, commercial MAO usually contains approximately 10 wt %trimethylaluminium (TMA), and commercial “modified MAO” (or “MMAO”)contains both TMA and TIBA. Quantities of alkylalumoxane are generallyquoted herein on a molar basis of aluminium (and include such “free”trialkylaluminium). The alkylalumoxane and/or alkylaluminium may beadded to the reaction media (i.e. ethylene and/or diluent and/orsolvent) prior to the addition of the catalyst or at the same time asthe catalyst is added. Such techniques are known in the art ofoligomerization and are disclosed in more detail in for example, U.S.Pat. Nos. 5,491,272; 5,750,817; 5,856,257; 5,910,619; and 5,919,996.

Examples of suitable organoboron compounds are boroxines, NaBH₄,trimethylboron, triethylboron,dimethylphenylammoniumtetra(phenyl)borate, trityltetra(phenyl)borate,triphenylboron, dimethylphenylammonium tetra(pentafluorophenyl)borate,sodium tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate,trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl) boron.

Activator compound (iii) may also be or contain a compound that acts asa reducing or oxidizing agent, such as sodium or zinc metal and thelike, or oxygen and the like.

In the preparation of the catalyst systems used in the presentinvention, the quantity of activating compound to be employed is easilydetermined by simple testing, for example, by the preparation of smalltest samples which can be used to oligimerize small quantities ofethylene and thus to determine the activity of the produced catalyst. Itis generally found that the quantity employed is sufficient to provide0.5 to 1000 moles of aluminium (or boron) per mole of chromium. MAO isthe presently preferred activator. Molar Al/Cr ratios of from 1/1 to500/1 are preferred.

Part B: Process Conditions

The chromium (component (i)) and ligand (component (ii)) may be presentin any molar ratio which produces oligomer, preferably between 100:1 and1:100, and most preferably from 10:1 to 1:10, particularly 3:1 to 1:3.Generally the amounts of (i) and (ii) are approximately equal, i.e. aratio of between 1.5:1 and 1:1.5.

Components (i)-(iii) of the catalyst system utilized in the presentinvention may be added together simultaneously or sequentially, in anyorder, and in the presence or absence of ethylene in any suitablesolvent, so as to give an active catalyst. For example, components (i),(ii) and (iii) and ethylene may be contacted together simultaneously, orcomponents (i), (ii) and (iii) may be added together simultaneously orsequentially in any order and then contacted with ethylene, orcomponents (i) and (ii) may be added together to form an isolablemetal-ligand complex and then added to component (iii) and contactedwith ethylene, or components (i), (ii) and (iii) may be added togetherto form an isolable metal-ligand complex and then contacted withethylene. Suitable solvents for contacting the components of thecatalyst or catalyst system include, but are not limited to, hydrocarbonsolvents such as heptane, toluene, 1-hexene and the like, and polarsolvents such as diethyl ether, tetrahydrofuran, acetonitrile,dichloromethane, chloroform, chlorobenzene, methanol, acetone and thelike.

The catalyst components (i), (ii) and (iii) utilized in the presentinvention can be unsupported or supported on a support material, forexample, silica, alumina, MgCl₂ or zirconia, or on a polymer, forexample polyethylene, polypropylene, polystyrene, or poly(aminostyrene).If desired the catalysts can be formed in situ in the presence of thesupport material, or the support material can be pre-impregnated orpremixed, simultaneously or sequentially, with one or more of thecatalyst components. The quantity of support material employed can varywidely, for example from 100,000 to 1 grams per gram of metal present inthe transition metal compound. In some cases, the support material canalso act as or as a component of the activator compound (iii). Examplesinclude supports containing alumoxane moieties.

The oligomerization can be, conducted under solution phase, slurryphase, gas phase or bulk phase conditions. Suitable temperatures rangefrom 10° C. to +300° C. preferably from 10° C. to 100° C., especiallyfrom 40° C. to 80° C. Suitable pressures are from atmospheric to 800atmospheres (gauge) preferably from 5 atmospheres to 100 atmospheres,especially from 10 to 50 atmospheres.

Irrespective of the process conditions employed, the oligomerization istypically carried out under conditions that substantially excludeoxygen, water, and other materials that act as catalyst poisons. Also,oligomerization can be carried out in the presence of additives tocontrol selectivity, enhance activity and reduce the amount of polymerformed in oligomerization processes. Potentially suitable additivesinclude, but are not limited to, hydrogen or a halide source.

There exist a number of options for the oligomerization reactorincluding batch, semi-batch, and continuous operation. The reactions ofthe present invention can be performed under a range of processconditions that are readily apparent to those skilled in the art: as ahomogeneous liquid phase reaction in the presence or absence of an inerthydrocarbon diluent such as toluene or heptanes; as a two-phaseliquid/liquid reaction; as a slurry process where the catalyst is in aform that displays little or no solubility; as a bulk process in whichessentially neat reactant and/or product olefins serve as the dominantmedium; as a gas-phase process in which at least a portion of thereactant or product olefin(s) are transported to or from a supportedform of the catalyst via the gaseous state. Evaporative cooling from oneor more monomers or inert volatile liquids is but one method that can beemployed to effect the removal of heat from the reaction. The reactionsmay be performed in the known types of gas-phase reactors, such ascirculating bed, vertically or horizontally stirred-bed, fixed-bed, orfluidized-bed reactors, liquid-phase reactors, such as plug-flow,continuously stirred tank, or loop reactors, or combinations thereof. Awide range of methods for effecting product, reactant, and catalystseparation and/or purification are known to those skilled in the art andmay be employed: distillation, filtration, liquid-liquid separation,slurry settling, extraction, etc. One or more of these methods may beperformed separately from the oligomerization reaction or it may beadvantageous to integrate at least some with the reaction; anon-limiting example of this would be a process employing catalytic (orreactive) distillation. Also advantageous may be a process whichincludes more than one reactor, a catalyst kill system between reactorsor after the final reactor, or an integrated reactor/separator/purifier.While all catalyst components, reactants, inerts and products could beemployed in the present invention on a once-through basis, it is ofteneconomically advantageous to recycle one or more of these materials; inthe case of the catalyst system, this might require reconstituting oneor more of the catalysts components to achieve the active catalystsystem. It is within the scope of this invention that an oligomerizationproduct might also serve as a solvent or diluent. Mixtures of inertdiluents or solvents also could be employed. The preferred diluents orsolvents are aliphatic and aromatic hydrocarbons and halogenatedhydrocarbons such as, for example, isobutane, pentane, toluene, xylene,ethylbenzene, cumene, mesitylene, heptane, cyclohexene,methylcyclohexene, 1-hexene, 1-octene, chlorobenzene, dichlorobenzene,and the like, and mixtures such as Isopar™.

Techniques for varying the distribution of products from theoligomerization reactions include controlling process conditions (e.g.concentration of components (i)-(iii), reaction temperature, pressure,residence time) and properly selecting the design of the process and arewell known to those skilled in the art.

The ethylene feedstock for the oligomerization may be substantially pureor may contain other olefinic impurities and/or ethane. One embodimentof the process of the invention comprises the oligomerization ofethylene-containing waste streams from other chemical processes or acrude ethylene/ethane mixture from a cracker.

It is also within the scope of the present invention to conduct anoligomerization reaction in the presence of two or more oligomerizationcatalysts. In one embodiment, all of the oligomerization catalysts maybe prepared with variants of the present novel P—N—P ligands. In anotherembodiment, a different form of oligomerization catalyst may be used incombination with a catalyst prepared from the present P—N—P ligands.

In a highly preferred embodiment of the present invention, theoligomerization product produced from this invention is added to aproduct stream from another alpha olefins manufacturing process forseparation into different alpha olefins. As previously discussed,“conventional alpha olefin plants” (wherein the term includes i) thoseprocesses which produce alpha olefins by a chain growth process using analuminum alkyl catalyst, ii) the aforementioned “SHOP” process and iii)the production of olefins from synthesis gas using the so called Lurgiprocess) have a series of distillation columns to separate the “crudealpha product” (i.e. a mixture of alpha olefins) into alpha olefins(such as butene-1, hexene-1 and octene-1). The mixed hexene-octeneproduct which is produced in accordance with the present invention ishighly suitable for addition/mixing with a crude alpha olefin productfrom an existing alpha olefin plant (or a “cut” or fraction of theproduct from such a plant) because the mixed hexene-octene productproduced in accordance with the present invention can have very lowlevels of internal olefins. Thus, the hexene-octene product of thepresent invention can be readily separated in the existing distillationcolumns of alpha olefin plants (without causing the large burden on theoperation of these distillation columns which would otherwise exist ifthe present hexene-octene product stream contained large quantities ofinternal olefins). As used herein, the term “liquid product” is meant torefer to the oligomers produced by the process of the present inventionwhich have from 4 to (about) 20 carbon atoms.

The liquid product from the oligomerization process of the presentinvention preferably consists of from 50 to 90 weight % linear hexenes(especially from 35 to 75 weight %) where all of the weight % isexpressed on the basis of the weight of liquid product. In view of thelarge amount of hexene produced, the oligomerization reaction of thisinvention may be referred to as a “trimerization”.

The preferred oligomerization process of this invention is alsocharacterized by producing very low levels of internal olefins (i.e. lowlevels of hexene-2, hexene-3, octene-2, octene-3 etc.), with preferredlevels of less than 10 weight % (especially less than 5 weight %) of thehexenes and octenes being internal olefins. Low levels of internalhexenes (e.g. hexene-2 and/or hexene-3) are highly desirable because:

-   -   a) internal hexenes generally have boiling points that are very        close to the boiling point of hexene-1 (and hence are difficult        to separate from hexene-1 by distillation); and    -   b) internal hexenes are difficult to copolymerize with ethylene        using conventional catalysts (in comparison to hexene-1) and        hence are not desired for use in most copolymerizations.

It is generally preferred to deactivate the oligomerization catalyst atthe end of the polymerization reaction. In general, many polar compounds(such as water, alcohols and carboxcylic acids) will deactivate thecatalyst. The use of alcohols and/or carboxcylic acids is preferred—andcombinations of both are contemplated.

It is also preferred to remove the catalyst (and by-product polymer, ifany) from the liquid product stream. Techniques for catalystdeactivation/product recovery that are known for use with otheroligomerization catalysts should also be generally suitable for use withthe present catalysts (see for example, U.S. Pat. Nos. 5,689,208 and5,340,785.

One embodiment of the present invention encompasses the use ofcomponents (i) (ii) and (iii) in conjunction with one or more types ofolefin polymerization catalyst system (iv) to trimerise ethylene andsubsequently incorporate a portion of the trimerisation product(s) intoa higher polymer.

Component (iv) may be one or more suitable polymerization catalystsystem(s), examples of which include, but are not limited to,conventional Ziegler-Natta catalysts, metallocene catalysts,monocyclopentadienyl or “constrained geometry” catalysts, phosphiniminecatalysts, heat activated supported chromium oxide catalysts (e.g.“Phillips”-type catalysts), late transition metal polymerizationcatalysts (e.g. diimine, diphosphine and salicylaldiminenickel/palladium catalysts, iron and cobalt pyridyldiimine catalysts andthe like) and other so-called “single site catalysts” (SSC's).

Ziegler-Natta catalysts, in general, consist of two main components. Onecomponent is an alkyl or hydride of a Group I to III metal, mostcommonly Al(Et)₃ or Al(iBu)₃ or Al(Et)₂Cl but also encompassing Grignardreagents, n-butyllithium, or dialkylzinc compounds. The second componentis a salt of a Group IV to VIII transition metal, most commonly halidesof titanium or vanadium such as TiCl₄, TiCl₃, VCl₄, or VOCl₃. Thecatalyst components when mixed, usually in a hydrocarbon solvent, mayform a homogeneous or heterogeneous product. Such catalysts may beimpregnated on a support, if desired, by means known to those skilled inthe art and so used in any of the major processes known forco-ordination catalysis of polyolefins such as solution, slurry, andgas-phase. In addition to the two major components described above,amounts of other compounds (typically electron donors) maybe added tofurther modify the polymerization behaviour or activity of the catalyst.

Metallocene catalysts, in general, consist of transition metalcomplexes, most commonly based on Group IV metals, ligated withcyclopentadienyl(Cp)-type groups. A wide range of structures of thistype of catalysts is known, including those with substituted, linkedand/or heteroatom-containing Cp groups, Cp groups fused to other ringsystems and the like. Additional activators, such as boranes oralumoxane, are often used and the catalysts may be supported, ifdesired.

Monocyclopentadienyl or “constrained geometry” catalysts, in general,consist of a transition metal complexes, most commonly based on Group IVmetals, ligated with one cyclopentadienyl(Cp)-type group, often linkedto additional donor group. A wide range of structures of this type ofcatalyst is known, including those with substituted, linked and/orheteroatom-containing Cp groups, Cp groups fused to other ring systemsand a range of linked and non-linked additional donor groups such asamides, amines and alkoxides. Additional activators, such as boranes oralumoxane, are often used and the catalysts may be supported, ifdesired.

A typical heat activated chromium oxide (Phillips) type catalyst employsa combination of a support material to which has first been added achromium-containing material wherein at least part of the chromium is inthe hexavalent state by heating in the presence of molecular oxygen. Thesupport is generally composed of about 80 to 100 wt. % silica, theremainder, if any, being selected from the group consisting ofrefractory metal oxides, such as aluminium, boria, magnesia, thoria,zirconia, titania and mixtures of two or more of these refractory metaloxides. Supports can also comprise alumina, aluminium phosphate, boronphosphate and mixtures thereof with each other or with silica. Thechromium compound is typically added to the support as a chromium (III)compound such as the acetate or acetylacetonate in order to avoid thetoxicity of chromium (VI). The raw catalyst is then calcined in air at atemperature between 250 and 1000° C. for a period of from a few secondsto several hours. This converts at least part of the chromium to thehexavalent state. Reduction of the Cr (VI) to its active form normallyoccurs in the polymerization reaction, but can be done at the end of thecalcination cycle with CO at about 350° C. Additional compounds, such asfluorine, aluminium and/or titanium may be added to the raw Phillipscatalyst to modify it.

Late transition metal and single site catalysts cover a wide range ofcatalyst structures based on metals across the transition series.

Component (iv) may also comprise one or more polymerization catalysts orcatalyst systems together with one or more additional oligomerizationcatalysts or catalyst systems. Suitable oligomerization catalystsinclude, but are not limited to, those that dimerise (for example,nickel phosphine dimerisation catalysts) or trimerise olefins orotherwise oligomerize olefins to, for example, a broader distribution of1-olefins (for example, iron and cobalt pyridyldiimine oligomerizationcatalysts).

Component (iv) may independently be supported or unsupported. Wherecomponents (i) and (ii) and optionally (iii) are supported, (iv) may beco-supported sequentially in any order or simultaneously on the samesupport or may be on a separate support. For some combinations, thecomponents (i) (iii) may be part or all of component (iv). For example,if component (iv) is a heat activated chromium oxide catalyst then thismay be (i), a chromium source and if component (iv) contains analumoxane activator then this may also be the optional activator (iii).

The components (i), (ii), (iii) and (iv) may be in essentially any molarratio that produces a polymer product. The precise ratio requireddepends on the relative reactivity of the components and also on thedesired properties of the product or catalyst systems.

An “in series” process could be conducted by first conducting theoligomerization reaction, then passing the oligomerization product to apolymerization reaction. In the case of an “in series” process variouspurification, analysis and control steps for the oligomeric productcould potentially be incorporated between the trimerization andsubsequent reaction stages. Recycling between reactors configured inseries is also possible. An example of such a process would be theoligomerization of ethylene in a single reactor with a catalystcomprising components (i)-(iii) followed by co-polymerization of theoligomerization product with ethylene in a separate, linked reactor togive branched polyethylene. Another example would be the oligomerizationof an ethylene-containing waste stream from a polyethylene process,followed by introduction of the oligomerization product back into thepolyethylene process as a co-monomer for the production of branchedpolyethylene.

An example of an “in situ” process is the production of branchedpolyethylene catalyzed by components (i)-(iv), added in any order suchthat the active catalytic species derived from components (i)-(iii) areat some point present in a reactor with component (iv).

Both the “in series” and “in situ” approaches can be adaptions ofcurrent polymerization technology for the process stages includingcomponent (iv). All major olefin existing polymerization processes,including multiple reactor processes, are considered adaptable to thisapproach. One adaption is the incorporation of an oligomerizationcatalyst bed into a recycle loop of a gas phase polymerization process,this could be as a side or recycle stream within the main fluidizationrecycle loop and or within the degassing recovery and recycle system.

Polymerization conditions when component (iv) is present can be, forexample, solution phase, slurry phase, gas phase or bulk phase, withtemperatures ranging from −100° C. to +300° C., and at pressures ofatmospheric and above, particularly from 1.5 to 50 atmospheres. Reactionconditions, will typically have a significant impact upon the properties(e.g. density, melt index, yield) of the polymer being made and it islikely that the polymer requirements will dictate many of the reactionvariables. Reaction temperature, particularly in processes where it isimportant to operate below the sintering temperature of the polymer,will typically, and preferably, be primarily selected to optimize thepolymerization reaction conditions. Also, polymerization orcopolymerization can be carried out in the presence of additives tocontrol polymer or copolymer molecular weights. The use of hydrogen gasas a means of controlling the average molecular weight of the polymer orcopolymer applies generally to the polymerization process of the presentinvention.

Slurry phase polymerization conditions or gas phase polymerizationconditions are particularly useful for the production of high or lowdensity grades of polyethylene, and polypropylene. In these processesthe polymerization conditions can be batch, continuous orsemi-continuous. Furthermore, one or more reactors may be used, e.g.from two to five reactors in series. Different reaction conditions, suchas different temperatures or hydrogen concentrations may be employed inthe different reactors.

Once the polymer product is discharged from the reactor, any associatedand absorbed hydrocarbons are substantially removed, or degassed, fromthe polymer by, for example, pressure let-down or gas purging usingfresh or recycled steam, nitrogen or light hydrocarbons (such asethylene). Recovered gaseous or liquid hydrocarbons may be recycled to apurification system or the polymerization zone.

In the slurry phase polymerization process the polymerization diluent iscompatible with the polymer(s) and catalysts, and may be an alkane suchas hexene, heptane, isobutane, or a mixture of hydrocarbons orparaffins. The polymerization zone can be, for example, an autoclave orsimilar reaction vessel, or a continuous liquid full loop reactor, e.g.of the type well-known in the manufacture of polyethylene by thePhillips Process. When the polymerization process of the presentinvention is carried out under slurry conditions the polymerization ispreferably carried out at a temperature above 0° C., most preferablyabove 15° C. Under slurry conditions the polymerization temperature ispreferably maintained below the temperature at which the polymercommences to soften or sinter in the presence of the polymerizationdiluent. If the temperature is allowed to go above the lattertemperature, fouling of the reactor can occur. Adjustment of thepolymerization within these defined temperature ranges can provide auseful means of controlling the average molecular weight of the producedpolymer. A further useful means of controlling the molecular weight isto conduct the polymerization in the presence of hydrogen gas which actsas chain transfer agent. Generally, the higher the concentration ofhydrogen employed, the lower the average molecular weight of theproduced polymer.

In bulk polymerization processes, liquid monomer such as propylene isused as the polymerization medium.

Methods for operating gas phase polymerization processes are well knownin the art. Such methods generally involve agitating (e.g. by stirring,vibrating or fluidizing) a bed of catalyst, or a bed of the targetpolymer (i.e. polymer having the same or similar physical properties tothat which it is desired to make in the polymerization process)containing a catalyst, and feeding thereto a stream of monomer (underconditions such that at least part of the monomer polymerizes in contactwith the catalyst in the bed. The bed is generally cooled by theaddition of cool gas (e.g. recycled gaseous monomer) and/or volatileliquid (e.g. a volatile inert hydrocarbon, or gaseous monomer which hasbeen condensed to form a liquid). The polymer produced in, and isolatedfrom, gas phase processes forms directly a solid in the polymerizationzone and is free from, or substantially free from liquid. As is wellknown to those skilled in the art, if any liquid is allowed to enter thepolymerization zone of a gas phase polymerization process the quantityof liquid in the polymerization zone is small in relation to thequantity of polymer present. This is in contrast to “solution phase”processes wherein the polymer is formed dissolved in a solvent, and“slurry phase” processes wherein the polymer forms as a suspension in aliquid diluent.

The gas phase process can be operated under batch, semi-batch, orso-called “continuous” conditions. It is preferred to operate underconditions such that monomer is continuously recycled to an agitatedpolymerization zone containing polymerization catalyst, make-up monomerbeing provided to replace polymerized monomer, and continuously orintermittently withdrawing produced polymer from the polymerization zoneat a rate comparable to the rate of formation of the polymer, freshcatalyst being added to the polymerization zone to replace the catalystwithdrawn from the polymerization zone with the produced polymer.

Methods for operating gas phase fluidized bed processes for makingpolyethylene, ethylene copolymers and polypropylene are well known inthe art. The process can be operated, for example, in a verticalcylindrical reactor equipped with a perforated distribution plate tosupport the bed and to distribute the incoming fluidizing gas streamthrough the bed. The fluidizing gas circulating through the bed servesto remove the heat of polymerization from the bed and to supply monomerfor polymerization in the bed. Thus the fluidizing gas generallycomprises the monomer(s) normally together with some inert gas (e.g.nitrogen or inert hydrocarbons such as methane, ethane, propane, butane,pentane or hexene) and optionally with hydrogen as molecular weightmodifier. The hot fluidizing gas emerging from the top of the bed is ledoptionally through a velocity reduction zone (this can be a cylindricalportion of the reactor having a wider diameter) and, if desired, acyclone and or filters to disentrain fine solid particles from the gasstream. The hot gas is then led to a heat exchanger to remove at leastpart of the heat of polymerization. Catalysts are preferably fedcontinuously or at regular intervals to the bed. At start up of theprocess, the bed comprises fluidizable polymer which is preferablysimilar to the target polymer. Polymer is produced continuously withinthe bed by the polymerization of the monomer(s). Preferably means areprovided to discharge polymer from the bed continuously or at regularintervals to maintain the fluidized bed at the desired height. Theprocess is generally operated at relatively low pressure, for example,at 10 to 50 atmospheres, and at temperatures for example, between 50 and135° C. The temperature of the bed is maintained below the sinteringtemperature of the fluidized polymer to avoid problems of agglomeration.

In the gas phase fluidized bed process for polymerization of olefins theheat evolved by the exothermic polymerization reaction is normallyremoved from the polymerization zone (i.e. the fluidized bed) by meansof the fluidizing gas stream as described above. The hot reactor gasemerging from the top of the bed is led through one or more heatexchangers wherein the gas is cooled. The cooled reactor gas, togetherwith any make-up gas, is then recycled to the base of the bed. In thegas phase fluidized bed polymerization process of the present inventionit is desirable to provide additional cooling of the bed (and therebyimprove the space time yield of the process) by feeding a volatileliquid to the bed under conditions such that the liquid evaporates inthe bed thereby absorbing additional heat of polymerization from the bedby the “latent heat of evaporation” effect. When the hot recycle gasfrom the bed enters the heat exchanger, the volatile liquid can condenseout. In one embodiment of the present invention the volatile liquid isseparated from the recycle gas and reintroduced separately into the bed.Thus, for example, the volatile liquid can be separated and sprayed intothe bed. In another embodiment of the present invention the volatileliquid is recycled to the bed with the recycle gas. Thus the volatileliquid can be condensed from the fluidizing gas stream emerging from thereactor and can be recycled to the bed with recycle gas, or can beseparated from the recycle gas and then returned to the bed.

A number of process options can be envisaged when using the catalysts ofthe present invention in an integrated process to prepare higherpolymers i.e. when component (iv) is present. These options include “inseries” processes in which the oligomerization and subsequentpolymerization are carried in separate but linked reactors and “in situ”processes in which a both reaction steps are carried out in the samereactor.

In the case of a gas phase “in situ” polymerization process, component(iv) can, for example, be introduced into the polymerization reactionzone in liquid form, for example, as a solution in a substantially inertliquid diluent. Components (i)-(iv) may be independently added to anypart of the polymerization reactor simultaneously or sequentiallytogether or separately. Under these circumstances it is preferred theliquid containing the component(s) is sprayed as fine droplets into thepolymerization zone. The droplet diameter is preferably within the range1 to 1000 microns.

Although not usually required, upon completion of polymerization orcopolymerization, or when it is desired to terminate polymerization orcopolymerization or at least temporarily deactivate the catalyst orcatalyst component of this invention, the catalyst can be contacted withwater, alcohols, acetone, or other suitable catalyst deactivators amanner known to persons of skill in the art.

A range of polyethylene polymers are considered accessible includinghigh density polyethylene, medium density polyethylene, low densitypolyethylene, ultra low density polyethylene and elastomeric materials.Particularly important are the polymers having a density in the range of0.91 to 0.93, grams per cubic centimeter (g/cc) generally referred to inthe art as linear low density polyethylene. Such polymers and copolymersare used extensively in the manufacture of flexible blown or cast film.

Depending upon the use of the polymer product, minor amounts ofadditives are typically incorporated into the polymer formulation suchas acid scavengers, antioxidants, stabilizers, and the like. Generally,these additives are incorporated at levels of about 25 to 2000 parts permillion by weight (ppm), typically from about 50 to about 1000 ppm, andmore typically 400 to 1000 ppm, based on the polymer. In use, polymersor copolymers made according to the invention in the form of a powderare conventionally compounded into pellets. Examples of uses for polymercompositions made according to the invention include use to form fibres,extruded films, tapes, spunbonded webs, molded or thermoformed products,and the like. The polymers may be blown or cast into films, or may beused for making a variety of molded or extruded articles such as pipes,and containers such as bottles or drums. Specific additive packages foreach application may be selected as known in the art. Examples ofsupplemental additives include slip agents, anti-blocks, anti-stats,mould release agents, primary and secondary anti-oxidants, clarifiers,nucleants, uv stabilizers, and the like. Classes of additives are wellknown in the art and include phosphite antioxidants, hydroxylamine (suchas N,N-dialkyl hydroxylamine) and amine oxide (such as dialkyl methylamine oxide) antioxidants, hindered amine light (uv) stabilizers,phenolic stabilizers, benzofuranone stabilizers, and the like.

Fillers such as silica, glass fibers, talc, and the like, nucleatingagents, and colourants also may be added to the polymer compositions asknown by the art.

The present invention is illustrated in more detail by the followingnon-limiting examples.

EXAMPLES

The following abbreviations are used in the examples:

Å=Angstrom units

NMR=nuclear magnetic resonance

Et=ethyl

Bu=butyl

iPr=isopropyl

H₂=hydrogen

Psi=pounds per square inch

c*=comparative

rpm=revolutions per minute

GC=gas chromatography

FID=Flame Ionization Detector

R_(x)=reaction

Wt=weight

C₄'s=butenes

C₆'s=hexenes (and 1-C₆=hexene-1)

C₈'s=octenes (and 1-C₈=octene-1)

PE=polyethylene

MAO=Methylalumoxane

Ligand Synthesis

General Experimental Conditions for Ligand Synthesis

All reactions involving air and/or moisture sensitive compounds wereconducted under nitrogen using standard Schlenk and glovebox techniques.Reaction solvents were purified using the system described by Pangbornet al (Pangborn, A. B. G., M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers,F. J., Organometallics 1996, 15, 1518 and then stored over activatedmolecular sieves. Diisopropylamine and 2-bromoanisole were purchasedfrom Aldrich and dried over 4 Å molecular sieves prior to use.1-Bromo-2-fluoro-benzene, phosphorus trichloride (PCl₃), hydrogenchloride gas and n-butyllithium were purchased from Aldrich and used asreceived. MAO, reported to be 10 wt % Al in toluene, was purchased fromAkzo and used as received. Deuterated solvents were purchased from CIL(toluene-d₈, THF-d₈) and were stored over 4 Å molecular sieves. NMRspectra were recorded on a Bruker 300 MHz spectrometer (300.1 MHz for¹H, 121.5 MHz for ³¹P, 282.4 for ¹⁹F).

Preparation of Et₂NPCl₂

Et₂NH (50.00 mmol, 5.17 mL) was added dropwise to a solution of PCl₃(25.00 mmol, 2.18 mL) in diethyl ether (“ether”) (200 mL) at −78° C.After the addition, the cold bath was removed and the slurry was allowedto warm to room temperature over 2 hours. The slurry was filtered andthe filtrate was pumped to dryness. The residue was distilled (500microns, 55° C.) to give the product in quantitative yield.

¹H NMR (δ, toluene-d₈): 2.66 (doublet of a quartets, 4H, J_(PH)=13 Hz,J_(HH)=7 Hz), 0.75 (triplet, 6H, J=7 Hz).

Ligand A Preparation of 2-Methoxyphenyl Lithium

To a solution of 2-bromoanisole (11.2 g, 60.08 mmol) in heptane (150 mL)was slowly added n-BuLi (1.6 M in hexenes, 36.7 mL). White precipitateformed. The slurry was stirred for 0.5 hrs and was filtered. The solidwas washed with pentane and was dried under vacuum. The yield was 6.5 g(94%).

Preparation of (2-MeO—C₆H₄)₂P—N(i-Pr)₂

An ether solution (30 mL) of i-Pr₂NPCl₂ (0.682 g, 3.375 mmol) was addedto 2-methoxyphenyl lithium (2-MeO—C₆H₄Li (0.77 g, 6.75 mmol) in ether(30 mL) at −70° C. The cold bath was removed and the reaction wasstirred for 1 hr at room temperature. The solid was filtered off and thefiltrate was pumped to dryness. The product was obtained in quantitativeyield. ¹H NMR (toluene-d8, δ): 7.48 (m, 2H), 7.14 (m, 2H), 6.88 (m, 2H),6.49 (m, 2H), 3.37 (septet, 2H), 3.25 (s, 6H), 1.16 (br s, 12H).

Preparation of (2-MeO—C₆H₄)₂PCl

HCl (g) was introduced into the head space of a 100 mL Schlenk flaskcontaining a stirred ether solution (30 mL) of (2-MeO—C₆H₄)₂P—N(i-Pr)₂made in the previous step. A precipitate formed immediately. Thepressure of HCl gas was maintained at 4 psi for 0.5 hrs. The slurry waspumped to dryness. The solid was extracted with toluene and the solventwas removed slowly under vacuum. The product crystallized while thesolution was evaporated to dryness. The crystalline solid was washedwith cold pentane (−70° C.) and was dried under vacuum. The yield was0.89 g (94%).

¹H NMR (toluene-d8, δ): 7.58 (m, 2H), 7.08 (m, 2H), 6.77 (m, 2H), 6.39(m, 2H), 3.20 (s, 6H).

Preparation of (2-MeO—C₆H₄)₂P[NH(i-Pr)]

An ether solution (30 ml) of (2-MeO—C₆H₄)₂PCl (0.45 g, 1.60 mmol) wasadded slowly to an ether solution (20 mL) of i-PrNH₂ (5 mL, 59 mmol) at−70° C. Immediate precipitate was observed. The cold bath was removedand the reaction was stirred at room temperature for 1.5 hrs. Thevolatiles were removed under vacuum and the solid was extracted withtoluene. The toluene solution was pumped to dryness to give thecrystalline product in quantitative yield (0.48 g).

¹H NMR (toluene-d8, δ): 7.67 (m, 2H), 7.11 (m, 2H), 6.91 (m, 2H), 6.42(m, 2H), 3.36 (septet, 1H), 3.24 (s, 6H), 2.20 (br.s, 1H), 1.12 (d, 6H,6.3 Hz).

Preparation of (2-MeO—C₆H₄)₂P[N(i-Pr)]P(2-F—C₆H₄) [Ligand A]

To a slurry of (2-MeO—C₆H₄)₂P[NH(i-Pr)] (0.498 g, 1.641 mmol) in pentane(25 mL) at −5° C. was added dropwise nBuLi (1.02 mL, 1.6 M in hexene).The white slurry became slightly yellow. After the slurry was vigorouslystirred for 40 mins, a pentane solution (20 mL) of (2-F—C₆H₄)₂PCl (0.466g, 1.81 mmol) was added. The ice/NaCl bath was removed and the reactionwas stirred at room temperature for 2 hrs and pumped to dryness.Dichloromethane (20 mL) was added to the solid. The resulting slurry wasstirred for 20 minutes and filtered. The filtrate was pumped to dryness.The residue was soaked with pentane (30 mL) to dissolve the excess of(2-F—C₆H₄)₂PCl. The pentane supernatant was decanted after standingstill at −50° C. for 2 hrs. The process was repeated (solid wasre-dissolved in dichloromethane, pumped to dryness, washed with pentane)to afford pure product in almost quantitative yield. The sticky solidcrystallized from toluene/heptane at room temperature to givecrystalline product (0.40 g).

¹H NMR (CD₂Cl₂, δ): 7.31 (m, 8H), 7.10 (m, 2H), 6.94 (m, 4H), 6.79 (m,2H), 3.87 (m, 1H), 3.63 (s, 6H), 1.20 (d, 6H, J=6.6 Hz).

¹⁹F NMR (CD₂Cl₂, δ): −105.41 (br s)

³¹P NMR (CD₂Cl₂, δ): 33.24 (br s), 24.61 (br.s)

Ligand B Preparation of (ortho-F—C₆H₄)P(NEt₂)₂

Ortho-F-bromobenzene (5.12 g, 29.23 mmol) in ether (50 mL) was addedwithin 1 hr to n-BuLi (18.27 mL of a 1.6M solution in hexenes) in ether(40 mL) at −85° C. (ethanol/liquid N2 bath). The temperature wasmaintained between −85° C. to −89° C. during the whole process. Thesolution was stirred for 2 more hrs at −85° C. to −89° C. Thetemperature of the cooling bath was lowered to −100° C. and (Et₂N)₂PCl(6.16 g, 29.23 mmol, prepared from the reaction of PCl₃ and four molarequivalents of Et₂NH) in 50 mL of ether was added. The reaction wasallowed to warm to room temperature within the cold bath overnight andwas pumped to dryness. The residue was extracted with pentane. Thepentane solution was pumped to dryness to give the product inquantitative yield. GC-MS, M⁺=270.

Preparation of (ortho-F—C₆H₄)PCl₂

To the head space of a 250 mL Schlenk flask containing a stirred ethersolution (60 mL) of (ortho-F—C₆H₄)P(NEt₂)₂ prepared in the last step wasintroduced HCl gas. The pressure of the gas was maintained under 4 Psiduring the 0.5 hr reaction time. The volatiles were removed under vacuumand the residue was extracted with pentane (3×50 mL). The filtrate waspumped under gentle vacuum to remove pentane. The remaining liquid wasdistilled under vacuum (300 microns, 35° C.-40° C. bath temperature)with dry ice cooling the receiver flask to avoid loss. The yield was 5.5g (96%).

¹H NMR (CD₂Cl₂, δ): 7.95 (m, 1H), 7.59 (m, 1H), 7.36 (m, 1H), 7.17 (m,1H)

¹⁹F NMR (CD₂Cl₂, δ): −108.68 (doublet of multiplets, J=81 Hz)

Preparation of (ortho-F—C₆H₄)(ortho-MeO—C₆H₄)PCl

To a vigorously stirred pentane solution (˜180 mL) of (ortho-F—C₆H₄)PCl₂(2.132 g, 10.77 mmol) at −70° C. was added dropwise an ether solution(50 mL) of ortho-MeO—C₆H₄Li (1.228 g, 10.77 mmol, prepared by a reactionof ortho-MeO—C₆H₄Br with n-BuLi in heptane at room temperature). Thecontent became a thick slurry. The reaction was warmed to roomtemperature in 2.5 hrs. The thick slurry became much thinner. The flaskwas moved to a glove box and the reaction was stirred at roomtemperature overnight. The content was filtered and the filtrate wasreduced in volume to about 5 mL. The product then began to crystallizeand was left to crystallize for 1 hr. The mother liquor was pipetted outand the crystals were washed with cold pentane (−70° C.), then driedunder vacuum. The yield was 2.67 g (93%).

¹H NMR (THF-d₈, δ): 7.61 (m, 1H), 7.42 (m, 2H), 7.28 (m, 1H), 7.10 (m,3H), 6.98 (m, 1H), 3.73 (s, 3H).

Preparation of (ortho-F—C₆H₄)(ortho-MeO—C₆H₄)PNH(i-Pr)

i-PrNH2 (2.3 ml) was added to an ether solution (30 mL) of(ortho-F—C₆H₄)(ortho-MeO—C₆H₄)PCl at room temperature. Immediateprecipitate was observed. The slurry was stirred for 1.5 hr and pumpedto remove volatiles. The residue was extracted with toluene andfiltered. Toluene was removed under vacuum to give an oil whichcrystallized at −60° C. in a freezer. The yield was quantitative.

¹H NMR (CD₂Cl₂, δ): 7.49 (m, 1H), 7.41 (m, 1H), 7.32 (m, 1H), 7.26 (m,1H), 7.11 (m, 1H), 6.99 (m, 1H), 6.93 (m, 1H), 6.82 (m, 1H), 3.65 (s,3H), 3.29 (m, 1H), 2.28 (br. t, 1H), 1.16 (d, 3H, J=6.6 Hz), 1.15 (d,3H, J=6.3 Hz).

Preparation of(ortho-F—C₆H₄)(ortho-MeO—C₆H₄)P[N(i-Pr)]P(ortho-F—C₆H₄)₂[Ligand B]

n-BuLi (1.38 ml of 1.6M hexenes solution, 2.212 mmol) was added dropwiseto a pentane solution (˜35 mL) of(ortho-F—C₆H₄)(ortho-MeO—C₆H₄)PNH(i-Pr) at −7° C. Precipitate wasobserved almost immediately. The slurry was stirred for 15 minutes. Apentane solution (˜30 mL) of (ortho-F—C₆H₄)₂PCl (0.624 g, 2.43 mmol) wasadded to the above mentioned slurry. The mixture was stirred at −6° C.for 5 minutes and was stirred at room temperature for 2 hrs. The slurrywas pumped to dryness. The solid was extracted with toluene and thetoluene solution was pumped to dryness. The residue was re-dissolved inpentane and the pentane solution was allowed to evaporate slowly to givea white crystalline solid (0.62 g). The mother liquor was pumped todryness to remove toluene completely. The residue crystallized fromheptane to give the second crop of product (0.29 g). The combined yieldwas 0.91 g (80%).

¹H NMR (CD₂Cl₂, δ): 7.45 (m, 1H), 7.32 (m, 7H), 7.10 (m, 3H), 6.93 (m,4H), 6.81 (m, 1H), 3.88 (m, 1H), 3.60 (s, 3H), 1.26 (d, 3H, J=6.3 Hz),1.16 (d, 3H, J=6.3 Hz)

¹⁹F NMR (CD₂Cl₂, δ): −105.46 (br. s, 1F), −105.54 (br.s, 1F), −106.45(d, J=54 Hz)

Ligand C Preparation of(ortho-F—C₆H₄)(ortho-MeO—C₆H₄)P[N(i-Pr)]P(ortho-F—C₆H₄)(ortho-MeO-C₆H₄

n-BuLi (1.04 mL of a 1.6M hexene solution) was added to pentane solution(30 mL) of (ortho-F—C₆H₄)(ortho-MeO—C₆H₄)PNH(i-Pr) (0.460 g, 1.67 mmol),which was previously cooled at −60° C. for 15 minutes. Precipitate wasobserved 1 minute after n-BuLi was added. The slightly yellowish slurrywas stirred for 15 minutes at room temperature. Solid(ortho-F—C₆H₄)(ortho-MeO—C₆H₄)PCl (0.459 g, 1.71 mmol) was then added tothe flask. The slurry became white and was left stirring in a glove boxfor 48 hrs. Volatiles were evaporated under vacuum. The solid wasextracted with toluene. The toluene solution was evaporated to about 1mL and pentane (20 mL) was added. Crystalline solid was collected after5 hours, washed with cold pentane and dried under vacuum. Pentane (10mL) was added to the mother liquor. More product crystallized after 16hours. ¹H NMR indicated that the two fractions contained two isomers ofthe title formula in different proportions. The combined yield was 0.45g (51%).

¹H NMR of fraction A (CD₂Cl₂, δ): 7.50 (m, 1.5H), 7.30 (m, 5H), 7.19 (m,1.5H), 7.04 (m, 2H), 6.93 (m, 4H), 6.79 (m, 2H), 3.83 (m, 1H), 3.57 (s,6H), 1.33 (d, 2.3H, J=6.4 Hz), 1.19 (d, 1.4H, J=5.6 Hz), 1.05 (d, 2.3H,J=6.4 Hz)

¹H NMR of fraction B (CD₂Cl₂, δ): 7.50 (m, 1H), 7.30 (m, 6H), 7.19 (m,1H), 7.04 (m, 2H), 6.93 (m, 4H), 6.79 (m, 2H), 3.83 (m, 1H), 3.58 (s,6H), 1.33 (d, 1.5H, J=6.4 Hz), 1.19 (d, 3H, J=5.6 Hz), 1.05 (d, 1.5H,J=6.4 Hz)

¹⁹F NMR of combined fractions (CD₂Cl₂, δ): −106.1 (br. m), −106.2 (br.m)

Preparation of (2,3-F₂—C₆H₃)₂P—NEt₂

To a solution of 1-bromo-2,3-difluorobenzene (5.0 g, 25.9 mmol) in ether(50 mL) was added n-BuLi (17.00 mL of 1.6 M n-BuLi hexene solution, 27.2mmol) dropwise over 1 hour at −78° C. The reaction was stirred for anadditional hour at −78° C. then Et₂NPCl₂ (2.3 g, 13.0 mmol) in ether (20mL) was added drop wise over 30 minutes resulting in purple colouredslurry. The reaction was allowed to warm to room temperature overnight.Volatiles were removed in vacuo and the residue was extracted withtoluene (3×10 mL) and the solution was pumped to dryness. The productwas isolated without further purification yielding a purple oil (4.0 g,94%).

¹H NMR (6, CD₂Cl₂): 7.24-7.02 (m, 6H), 3.07 (d of q, 4H, J_(PH)=13 Hz,J_(HH)=7 Hz), 0.97 (triplet, 6H, J_(HH)=7 Hz). ¹⁹F NMR (δ, CD₂Cl₂):−132.88 (d of m, J=42 Hz), −140.35 (m).

Preparation of (2,3-F—C₆H₃PCl

A solution of HCl in ether (1.0M, 30.0 mL, 30 mmol) was added rapidly toan ethereal solution (25 mL) of (2,3-F₂—C₆H₄)₂P—NEt₂ (3.8 g, 11.5 mmol)over a 1 hour period at 0° C. A white precipitate formed immediately andthe solution lightened to a yellow colour. The reaction was warmed toroom temperature and stirred for an additional 4 hrs at which pointslurry was pumped to dryness to remove volatiles. The residue wasre-slurried in ether (50 mL), filtered, washed (2×25 mL) and pumped todryness affording a brown oil (2.96 g, 88%).

Note: Recrystallization from pentane afforded a solid material.

¹H NMR (δ, CDCl₃): 7.40-7.16 (m, 6H); ³¹P NMR (δ, CDCl₃): 57.9 (t, J=56Hz).

Preparation of (2,3-F₂—C₆H₃)₂PNH(i-Pr)

To a solution of —PrNH₂ (0.5 mL, 5.6 mmol) and NEt₃ (2.2 mL, 15.4 mmol)in ether (50 mL) was added an ethereal solution (20 mL) of(2,3-F₂—C₆H₄)PCl (1.00 g, 3.90 mmol) at 0° C. Immediate precipitate wasobserved. The slurry was stirred for 3 hours, filtered and washed (3×10mL) with ether. The filtrate was pumped to dryness yielding a brown oil(1.58 g, 98%). ¹H NMR (δ, CDCl₃): 7.29 (m, 2H), 7.11 (m, 4H), 3.36(septet, 1H, J=7 Hz), 2.26 (brs, 1H), 1.19 (d, 6H, J=7 Hz)l; ³¹P NMR (δ,CDCl₃): 16.4 (m).

Preparation of (2,3-F₂—C₆H₃)₂PN(i-Pr)P(ortho-MeO—C₆H₄)₂

To a solution of (ortho-MeO—C₆H₄)₂PNH(i-Pr) (0.33 g, 1.09 mmol) inpentane (20 mL) maintained at −5° C. was added drop wise a solution ofn-BuLi (0.68 mL of 1.6 M n-BuLi hexene solution, 1.09 mmol) leaving ayellow slurry. The mixture was stirred at −5° C. for 15 minutes followedby slow addition an ethereal solution (10 mL) of (2,6-F—C₆H₄)₂PCl (0.32g, 1.10 mmol). The now white slurry was stirred for 30 minutes at −5°C., and then allowed to slowly warm to room temperature stirring for anadditional 3 hours. Volatiles were removed from the solution in vacuoand the residue was extracted into toluene, filtered, washed (3×10 mL)and dried leaving a pale peach pasty solid. The crude product wastriturated with pentane to afford a solid, which was recrystallized fromheptane at −65° C. yielding a white solid product (0.35 g, 57%).

¹H NMR (δ, CD₂Cl₂): 7.33 (m, 2H), 7.26-7.07 (m, 8H), 6.83 (m, 2H), 6.81(m, 2H), 3.86 (br. m, 1H), 3.64 (s, 6H), 1.21 (d, J=6 Hz, 6H); ¹⁹F NMR(6, CD₂Cl₂): −131.7 (br.)), −140.6 (br.).

Trimerization Reactions Example 1

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.74 g, 10 wt % MAO in toluene) in 63.26 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 45° C. Ligand A (17.58 mg, 0.0357 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.52 mg, 0.0329mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 27.5 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor, cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol and then weighed. The massof product produced (52.1 g) was taken as the difference in weightsbefore and after the reactor contents were added to the flask with theethanol. A sample of the liquid product was analyzed by GC-FID. (Example1, Table 1).

Example 2

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.75 g, 10 wt % MAO in toluene) in 63.25 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (32 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 55° C. Ligand A (17.52 mg, 0.0356 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.59 mg, 0.0332mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 16 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor, cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (58.2 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 2, Table1).

Example 3

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.75 g, 10 wt % MAO in toluene) in 63.25 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (29 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 65° C. Ligand A (17.63 mg, 0.0359 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.64 mg, 0.0333mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 12.5 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (65.7 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 3, Table1).

Example 4

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.76 g, 10 wt % MAO in toluene) in 63.24 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (17 psig) and ethylene (15 atmospheres (gauge)) and thetemperature adjusted to 65° C. Ligand A (17.42 mg, 0.0359 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.49 mg, 0.0333mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 20 atmospheres (gauge).The reaction was terminated after 20 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (36.9 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 4, Table1).

Example 5

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.74 g, 10 wt % MAO in toluene) in 63.26 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 75° C. Ligand A (17.47 mg, 0.0355 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.54 mg, 0.0330mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 11.5 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (65.3 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 5, Table1).

Example 6

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.80 g, 10 wt % MAO in toluene) in 63.20 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 45° C. Ligand B (17.23 mg, 0.0355 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.65 mg, 0.0334mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 9.4 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (86.1 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 6, Table1).

Example 7

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (3.26 g, 10 wt % MAO in toluene) in 65.74 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 45° C. Ligand B (10.05 mg, 0.0197 mmol) in 8.69g of toluene was added to chromium acetylacetonate (6.48 mg, 0.0186mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 16.7 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (93.4 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 7, Table1).

Example 8

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (3.55 g, 10 wt % MAO in toluene) in 65.45 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 75° C. Ligand B (10.49 mg, 0.0205 mmol) in 8.69g of toluene was added to chromium acetylacetonate (7.13 mg, 0.0204mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 11.7 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (63.8 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 8, Table1).

Example 9

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (5.74 g, 10 wt % MAO in toluene) in 63.26 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 45° C. Ligand C (15.54 mg, 0.0296 mmol) in 8.69g of toluene was added to chromium acetylacetonate (11.64 mg, 0.0333mmol) in 8.68 g of toluene in a hypovial. The mixture was transferredunder ethylene to the pressurized reactor. Immediately after, ethylenewas added to increase the reactor pressure to 40 atmospheres (gauge).The reaction was terminated after 15 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (64.3 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 9, Table1).

Example 10

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (2.88 g, 10 wt % MAO in toluene) in 66.12 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 75° C. Ligand C (8.61 mg, 0.0164 mmol) in 8.69 gof toluene was added to chromium acetylacetonate (5.75 mg, 0.0165 mmol)in 8.68 g of toluene in a hypovial. The mixture was transferred underethylene to the pressurized reactor. Immediately after, ethylene wasadded to increase the reactor pressure to 40 atmospheres (gauge). Thereaction was terminated after 11.04 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (65.4 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 10, Table1).

Example 11

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (2.90 g, 10 wt % MAO in toluene) in 66.10 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (35 psig) and ethylene (35 atmospheres (gauge)) and thetemperature adjusted to 45° C. Ligand C (8.68 mg, 0.0165 mmol) in 8.69 gof toluene was added to chromium acetylacetonate (5.77 mg, 0.0165 mmol)in 8.68 g of toluene in a hypovial. The mixture was transferred underethylene to the pressurized reactor. Immediately after, ethylene wasadded to increase the reactor pressure to 40 atmospheres (gauge). Thereaction was terminated after 30 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (49.7 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 11, Table1).

Example 12

A 600-mL reactor fitted with a stirrer (1700 rpm) was purged 3 timeswith argon while heated at 80° C. The reactor was then cooled to 30° C.and a solution of MAO (2.87 g, 10 wt % MAO in toluene) in 66.13 g oftoluene was transferred via a stainless steel cannula to the reactor,followed by 86.7 g of toluene. The reactor was then pressurized withhydrogen (20 psig) and ethylene (15 atmospheres (gauge)) and thetemperature adjusted to 45° C. Ligand C (8.63 mg, 0.0165 mmol) in 8.69 gof toluene was added to chromium acetylacetonate (5.72 mg, 0.0164 mmol)in 8.68 g of toluene in a hypovial. The mixture was transferred underethylene to the pressurized reactor. Immediately after, ethylene wasadded to increase the reactor pressure to 20 atmospheres (gauge). Thereaction was terminated after 30 minutes by stopping the flow ofethylene to the reactor and cooling the contents to 30° C., at whichpoint excess ethylene was slowly released from the reactor cooling thecontents to 0° C. The product mixture was transferred to a pre-weighedflask containing approximately 1 g of ethanol. The mass of productproduced (18.6 g) was taken as the difference in weights before andafter the reactor contents were added to the flask with the ethanol. Asample of the liquid product was analyzed by GC-FID. (Example 12, Table1).

TABLE 1 Hexene and Octene Contents in Mixture Selectivity Other ProductsExam- P 1-C₆ total 1-C₈ total (1-C₆ + 1-C₆ 1-C₈ Produc- PE Ligand ple T°C. (bar) % C_(6′S) % C_(8′S) 1-C₈) % % % tivity** C_(4′S) C₁₀ C₁₂ C₁₂₊wt % Ligand A 1 45 40 68.7  68.84 24.59 24.77 93.3  99.8  99.26 66,3002.16 1.23 0.83 2.18 0.00 Ligand A 2 55 40 79.53 79.63 15.49 15.63 95.0299.87 99.1 126,550 1.39 0.97 0.67 1.71 0.00 Ligand A 3 65 40 87.24 87.319.01 9.12 96.32 99.92 98.79 181,960 0.8  0.71 0.51 1.55 0.30 Ligand A 465 20 85.9  85.95 7.24 7.39 93.14 99.94 97.97 64,707 1.59 1.37 1.02 2.680.27 Ligand A 5 75 40 90.85 90.9  5.96 6.07 96.81 99.94 98.19 198,3480.56 0.57 0.42 1.48 0.15 Ligand B 6 45-70-55 40 83.00 83.18 15.29 15.3898.29 99.78 99.41 316,932 0.04 0.18 0.12 1.11 0 Ligand B 7 45 40 75.2675.50 22.87 22.98 98.13 99.68 99.52 347,915 0.05 0.18 0.17 1.13 0 LigandB 8 75 40 88.80 88.92 10.32 10.43 99.12 99.86 98.94 309,173 0.06 0.090.05 0.46 0 Ligand C 9 45 40 85.38 85.47 12.02 12.08 97.40 99.89 99.5148,402 0.22 0.35 0.14 1.74 0 Ligand C 10 75 40 94.39 94.42 3.86 3.9098.25 99.96 98.97 415,519 0.16 0.24 0.12 1.16 0 Ligand C 11 45 40 83.3683.46 14.22 14.27 97.58 99.88 99.65 115,738 0.21 0.34 0.15 1.57 0 LigandC 12 45 20 89.65 89.72 8.87 8.95 98.52 99.92 99.1 43,664 0.18 0.27 0.090.78 0 **unit in g product/gCr hr Ligand AiPr—N[P(2-F—C6H4)2][P(2-OMe—C6H4)2] Ligand B(2-F—Ph)2P—N(iPr)—P(2-OMe—Ph)(2-F—Ph) Ligand C(2-F—Ph)(2-OMe—Ph)P—N(iPr)—P(2-OMe—Ph)(2-F—Ph)

1. A ligand defined by the formula:

wherein each of Ph₁, Ph₂, Ph₃ and Ph₄ is a phenyl group bonded to aphosphorus atom, with the provisos that i) at least one of Ph₁, Ph₂, Ph₃and Ph₄ is ortho substituted with a halogen selected from the groupconsisting of fluorine, bromine and chlorine; ii) at least one of Ph₁,Ph₂, Ph₃ and Ph₄ is ortho substituted with a polar substituent; and iii)R₂ is selected from the group consisting of hydrogen, C₁₋₂₀ hydrocarbyland silyl.
 2. The ligand of claim 1 wherein said polar substituent is aC₁₋₂₀ alkoxy.
 3. The ligand of claim 1 wherein said halogen is fluorine.4. The ligand of claim 1 wherein R₂ is a C₁₋₄ hydrocarbyl.
 5. The ligandof claim 3 wherein R is isopropyl.
 6. A catalyst system comprising: a) atransition metal selected from the group consisting of Cr, V, Ti, Ni,and W; b) A ligand defined by the formula:

wherein each of Ph₁, Ph₂, Ph₃ and Ph₄ is a phenyl group bonded to aphosphorus atom, with the provisos that i) at least one of Ph₁, Ph₂, Ph₃and Ph₄ is ortho substituted with a halogen selected from the groupconsisting of fluorine, bromine and chlorine; ii) at least one of Ph₁,Ph₂, Ph₃ and Ph₄ is ortho substituted with a polar substituent; and iii)R₂ is selected from the group consisting of hydrogen, C₁₋₂₀ hydrocarbyland silyl; and c) an activator.
 7. A process for the oligomerization ofethylene comprising contacting the catalyst system of claim 6 withethylene under oligomerization conditions.
 8. The process of claim 7when undertaken at a temperature of from about 10° C. to 300° C. and apressure of from 5 to 100 atmospheres.
 9. The process of claim 7 whereinsaid transition metal is Cr.
 10. The process of claim 7 wherein saidactivator is methylaluminoxane.
 11. The process of claim 7 which isfurther characterized by producing a liquid product stream whichcontains from 50 to 90 weight % linear hexenes.
 12. The process of claim11, further characterized in that said linear hexenes contain less than10 weight % internal hexenes.